The purpose of the proposed study is to define the functions of a putative neurotransmitter/neuromodulator substance, the peptide somatostatin (SRIF) by comparing the hodology of the SRIF system in the rat with that found in the squid, Loligo pealeii. Ongoing studies in the P/I's laboratory have shown that in the rodent this peptide probably participates in a large number of different neuronal systems, yet no clear-cut function for SRIF in the CNS has emerged. Preliminary studies in the P/I's laboratory, which were begun when the P/I was in residence at M.B.L., have demonstrated a widespread but somewhat more restricted distribution for SRIF in the cephalopod mollusk Loligo pealeii, the Wood's Hole squid. In this one-year proposal the P/I will describe the SRIF system in the squid and compare the neuroanatomy of this peptide in the invertebrate with that seen in the rat. Using light-microscopic immunocytochemistry alone and in combination with modern anatomical techniques for pathway tracing in mammals, i.e., retrograde transport of HRP and anterograde transport of 3H-amino acids, we will describe, in Loligo: distribution, morphology and projections of SRIF neurons. We shall compare these results with those in the rat to determine if, in evolution, there is a preferential association of SRIF with visceral, motor, or sensory systems. The results of this analysis will enable us to: 1) restructure our thinking of the role of SRIF systems in the mammalian CNS; 2) describe the biochemical, as well as morphological, evolution of the CNS; and 3) eventually allow us to establish rules for the integration of autonomic and cognitive functions.